In that case every possible way of collecting randomness is a scheme. What is probing /dev/urandom everytime you need a random number, if not a scheme?

Obviously, gmaxwel's quote was refering to a simple deterministic function whose input is a known literary work, I'll agree that if it is simple to memorize such a scheme, then it is quite likely that other people could come up with it, then running it against known corpora is a matter of having the resources to do so. Such resources are relatively accessible nowadays.

A sentence from a book, regardless the language is a very bad idea, but it is not a relevant example in the context of this thread.